In treating certain serious diseases, frequent injections of various drugs are required. Often these injections must be given venously or arterially, or by other means, so as to ensure local and precise distribution of the drugs used in treatment. In order to avoid inserting and withdrawing a catheter when each injection is administered, for many years now recourse has been had to implantable drug-dispensing capsules, placed under the patient's skin at a suitable point, and whose inner body communicates with a tube left in place in the body and emerging at the point where the injections are to be given. The capsule has a perforatable wall through which it is possible to inject the drug to be dispensed by means of a needle, the wall closing up again automatically when the needle is withdrawn.
Generally speaking, and as it is understood in this field of application, a serious, fundamental problem presents itself with regard to the assurance that must be given to the practitioner that the needle is correctly introduced into the inner body of the dispensing capsule. Indeed, some of the drugs used may be of doubtful efficacy and cause the patient's death, or serious mishaps, if the drug injection, by mistake, is not made inside the body of the capsule and spreads, for example, between the capsule and the skin covering it.
In some systems for registering the proper introduction of the needle of the injection syringe into the body of the drug-dispensing capsule, this same capsule is placed in contact by its outer wall with the patient's body and has an electrically conducting inner wall forming a detection device near the end of this needle. In addition, it is known that the registering system can be equipped with an external signaling apparatus, connected to the aforementioned detection device, which responds to the closing through the patient's body of an electrical circuit that includes the inner conducting wall of the aforementioned capsule and the needle.
Such systems nonetheless present a certain number of drawbacks.
Indeed, it has been recognized that, together with the fundamental problem regarding assurance of proper introduction of the needle, practical difficulties were posed for the application and utilization of the known systems. More precisely, it was noted that the signaling device that alerts the practitioner to the correct introduction of the needle was sometimes prematurely triggered while the needle was still not in contact with the bottom of the capsule. A slight variation in impedance, too rapid, could trip the device, understandably posing a real danger to the patient.